DESCRIPTION (provided by candidate): I seek funding to extend my training in environmental health science and developmental toxicology by acquiring additional expertise in three areas: human embryonic stem cell (hESC) biology, molecular biology, and bioinformatics. Learning laboratory-based methods and statistical approaches used in these three areas will provide me with the skills that are required to transition into an independent academic career, investigating how environmental exposures alter early human embryogenesis, and their potential contributions to childhood and adult diseases. For the K99 phase, my primary mentor is Dr. Susan Fisher, whose expertise includes using hESC models for studying human development. I will also receive valuable input from my other mentors who are leaders in the fields of human neuronal development, prenatal environmental exposures, and bioinformatics. I will obtain extensive training in hESC biology, methods for differentiating these cells into neurons, and approaches for studying the effects of toxicants on this process. HESCs are a valuable model of human embryogenesis because they develop into the three primary germ layers and their derivatives such as neurons. Additionally, I will learn state-of-the-art technique for investigating the transcriptome, e.g., RNA- sequencing (RNA-seq). In general, I theorize that specific environmental exposures during pregnancy impact hESC self-renewal and/or one or more steps in their differentiation to neurons, resulting in detrimental developmental and neurobehavioral outcomes. Here, I aim to test the specific hypothesis that, at environmentally relevant levels, polybrominated diphenyl ethers (PBDE), widely-used flame retardants and potential neurodevelopmental toxicants, disrupt human neurogenesis. First, using an hESC model of neuronal differentiation, I will establish the relevant effective doses of congeners PBDE-47 and/or PBDE-99 (Aim 1). Second, honing in on the relevant ranges, I will characterize the dose-dependent effects of PBDEs at the level of the transcriptome (Aim 2). Finally, I will determine the functional relevance of PBDE gene targets in terms of hESC self-renewal and/or neuronal development (Aim 3). The proposed experiments are the first investigation of PBDE effects on hESCs and their neuronal derivatives. The expected result is identification of alterations at the level of the transcriptome and a functional analysis of genes whose expression levels change. Subsequently, this work could lead to several new research directions. For example, gene-environment interactions identified in vitro could be validated, in terms of adverse neurodevelopmental outcomes, using in vivo models. Additionally, it will be interesting to learn if the PBDE targets are specific to these chemicals or more broadly indicative of neurodevelopmental toxicity. My primary mentor and co-mentors, in complementary fields, will guide me in learning the techniques required to carry out the proposed research. By completing this project, I will master powerful approaches that will enable me to reach my ultimate goal of studying, as an independent investigator, the effects of potential toxicants on seminal aspects of early human development.